(Reuters) - It may be only a "dumb" fence, but it´s a big one. Israel
hopes it will protect the remote Sinai border from infiltration by
enemies exploiting the wandering ways of Bedouin tribes and a
perceived surge in lawlessness following Egypt´s political upheavals.

When it is finished in 2013, the 5-metre (16-foot) high barrier of
galvanized steel bars and razor mesh -- at this stage minus the smart
electronic sensors used elsewhere -- will run most of the 266 km (165
miles) from Eilat on the Red Sea´s Gulf of Aqaba up to the already-
closed Gaza Strip on the Mediterranean.

For much of its course, the silvery steel fence weaves up and down
among the barren brown hills beside Route 12, a lonely two-lane
blacktop through the desert that was closed to traffic after gunmen
crossed the border last August and attacked a bus, killing eight
Israelis.

On Sunday, the Israel Defense Forces (IDF) announced that the fence
had already improved security to the point where Route 12 could now
be reopened, although in daylight hours only.

Like no other country in the world Israel is fenced off, to the north
with Lebanon and Syria, to the east with Jordan, in the centre by a
barrier partly of high concrete walls enclosing the occupied West
Bank, and now to the west with Egypt.

"This is a hot border now," said IDF Lt. Col Yoav Tilan at the fence,
where welders, pile-drivers and tractors were at work in the empty
desert.

On the Lebanon border Israel faces a rocket threat from the Lebanese
Shiite Hezbollah movement. On the blockaded Gaza Strip a fortified
front line separates Israeli forces from Gaza´s armed Palestinian
Islamist group, Hamas. The Jordan River valley is fenced and
patrolled along its length.

The landmines, movement detectors and heat sensors that enhance the
protective power of Israel´s border fences elsewhere are not yet
installed on the Sinai barrier. IDF Bedouin trackers daily inspect a
path smoothed in the sand for any sign of nighttime infiltrations.

"This is what we call a dumb fence. It is only one part of our
defensive suite," Tilan told reporters on a tour. "It has already
been cut once. But they didn´t get through."

SINAI HAS CHANGED

Sinai was relatively quiet for 30 years, but a rapid increase in the
flow of migrants from Africa since the mid-2000s highlighted how easy
it was to cross the border.

The situation has only become worse after Egypt´s revolution a year
ago relaxed the grip of the Cairo authorities on Sinai´s desert
tribes.

Israel´s primary concern then and now is that its enemies will
exploit any security lapses. Israel says Egypt´s security forces have
been paying less attention to Sinai since President Hosni Mubarak was
overthrown in February 2011, opening the door to lawlessness that
helps terrorist organizations.

Israeli military authorities say Palestinian militants in Gaza, led
by Hamas but including Islamic Jihad, are trying to use the peninsula
as a back door.

"The fence is part of a security concept intended to stop
infiltrations and terror activity in the country," said Brig-Gen Eran
Ofir, who heads the 1.3-billion-shekel ($380-million) project. It was
first authorized in January 2010 but construction began only in
November of that year.

On August 18, 2011, eight Israelis were killed on Route 12 by
militants who crossed the unfenced border with automatic weapons and
rocket-propelled grenades. Three attackers and five Egyptian soldiers
were killed in the ensuing gun battle with the IDF, igniting furious
protests outside the Israeli embassy in Cairo.

The IDF says Palestinian gunmen carried out the attack.

"We believe there are other groups with the same plans right now. We
could face another terror attack at any time," said an Israeli
commander who briefed reporters at the IDF´s regional command post on
Route 12. "There is a constantly increasing threat from the Western
border, turning into a hostile terror threat."

The IDF says it must treat any criminal activity on the border
initially as a terrorist threat. Last Wednesday, it said a border
patrol chased off smugglers and found a bomb.

"A smuggling attempt was identified, and the force that operated to
stop the smuggling identified a man hurling a suspicious bag and
escaping from the scene," the IDF said. "It was discovered the bag
contained a powerful explosive device."

This was a reminder that smuggling routes over the border "are
constantly being used by terror organizations", it said.

There have been no lethal attacks since August, however.

The commander, who asked not to be named, said cooperation with Egypt
is good. Liaison officers talk daily and commanders meet in person
every two weeks or so. But Israel hopes that as Egypt is stabilized,
it will put more into policing the desert.

Israel says while it has increased manpower on the border, Egypt´s
force is two battalions below permitted strength.

"The quality of intelligence is very low," the officer said.

BORDER MOSTLY EMPTY

Some 55,000 migrants have entered Israel from Sinai since 2006, and
the flow is accelerating. In all of 2006 there were 2,777. In the
past quarter they averaged about 2,500 per month.

People-smugglers equipped with 4x4s and night-vision scopes deliver
them to the rocky ridges north of Eilat. They make no effort to
escape once they reach Israel but surrender to the IDF, hoping to be
processed as asylum seekers.

The Israeli commander said 90 percent of Africans infiltrating Israel
are economic migrants seeking a better life. Many of the migrants are
educated city dwellers with skills and even professional
qualifications, he said.

Their journeys are well organized by companies specializing in the
trade and typically begin with a flight from Eritrea to Cairo, from
where they cross the Suez Canal by road into the Sinai peninsula,
completing the final trip to the border over desert tracks at night.
It takes about two and a half days.

"The Bedouin smugglers are excellent drivers by day or night. They
can outrun us in most places and they know the terrain very well,"
the commander said.

Thousands of migrants in legal limbo gravitate to the gray economy of
the interior. Israel recently adopted stiff penalties to deter the
influx, permitting detention for up to three years, to make the point
that the country is not a soft route to Europe.